This invention relates to a variable spring constant type damper filled with viscous fluid which is a vibration isolator for damping external vibration in acoustic instruments and information instruments using an optical disk or the like.
The viscous fluid sealed-type damper damps an external vibration transmitted to a supported body 10 through viscous flow resistance. A stirring portion 3 accepting a shaft 4 is installed on the supported body 10 and oscillates in a viscous fluid 2 in a cylindrical container 1 with a flexible portion 9 made of an elastic body like rubber as is illustrated in FIG. 12.
External vibration can act on acoustic and information instruments using an optical disk or the like, at a frequency and/or an acceleration from small to large, and an impact action. A vibration effect is adjusted by changing the viscosity of the fluid in the viscous fluid sealed-type damper and the hardness of the elastic body like rubber of the supported body, for various vibrations with consideration of weight and balance of the supported body.
The apparent dynamic spring becomes high when sealing the high-viscosity fluid in the case of adjusting a vibration-isolating effect by the viscosity of the fluid, and its amplitude can be reduced by a high resonance frequency and a high damping force. However, the resonance frequency and the damping force are high for a high frequency of 100 Hz or more, whereby a reduction effect of a vibration transmissibility is low, that is to say, the vibration-isolating effect is reduced.
In contrast with this, since a resonance magnification of the supported body becomes high at the vicinity of the resonance frequency (in particular, the vicinity of the low frequency of 10 to 20 Hz) of the supported body when sealing the low viscosity fluid, the amplitude of the supported body becomes large, and a sound divergence of the disk and malfunctions tend to occur at the vicinity of this frequency because of an impact due to a collision of the supported body with a chassis for supporting a disk and an impact due to a collision of the stirring portion with the container or a cap, whereby it has been difficult to obtain the viscous fluid sealed-type damper having a great damping effect over a wide frequency band from a low frequency band to a high frequency band in adjustment of the viscosity of the fluid, and suppressing the resonance magnification at the resonance frequency of the supported body.
Moreover, adjusting the vibration isolating effect by changing the hardness of the rubber of the flexible portion of the elastic body like rubber is very difficult in the fine adjustment, and molding failures such as a weld are caused since a flowability of the material is changed.
This invention is devised in order to solve the problems described above, and provides a variable spring constant type damper filled with viscous fluid constituted to allow the spring constant to depend upon the amplitude by giving changes to the wall thickness of the flexible portion of the damper. Since a thin walled portion oscillates mainly when the amplitude is relatively small, only the spring constant of the thin-walled portion exerts an influence upon the spring constant of the entire damper. Since a thick-walled portion oscillates when the amplitude is relatively large, the spring constant of the thick-walled portion exerts a influence upon the spring constant of the entire damper. Therefore, since the spring constant is small in a high-frequency band with small amplitude, the vibration transmissibility can be lower, and the spring constant is large in a low-frequency band large in amplitude, whereby a resonance magnification can be lower.
Moreover, the variable spring constant type damper filled with viscous fluid is provided where the flexible portion is not broken in practical use, which is large in securing strength between the flexible portion and the cylindrical portion, and has high reliability.
Namely, this invention provides a variable spring constant type damper filled with viscous fluid in which the viscous fluid is sealed by the container. The container is constituted by the stirring portion, the cylindrical portion and the flexible portion made of the elastic body like rubber connecting both the siring and cylindrical portions and the cap. The vibration damping is performed with the viscous resistance caused by the traveling of the stirring portion in the viscous fluid in response to the external vibration in which the wall thickness of the flexible portion is varied.
Furthermore, this invention provides a variable spring constant type damper filled with viscous fluid in which the changes of the wall thickness of the flexible portion are formed so as to vary between a thick wall thickness or thin wall thickness toward the cylindrical portion from the stirring portion successively or in stages.
Furthermore, this invention provides a variable spring constant type damper filled with viscous fluid in which the wall thickness of the flexible portion has a step toward the cylindrical portion and its change is formed such that the thickness can be switched.
Furthermore, this invention provides a variable spring constant type damper filled with viscous fluid wherein the ratio of the thin wall thickness versus the thick wall thickness of the flexible portion is 1.0:1.1 to 1.0:5.0.
Moreover, the wall thickness of the flexible portion is formed so as to become thin toward the central portion from the periphery of the connection of the stirring portion and the cylindrical portion successively or in stages.
Furthermore, the flexible portion is formed such that the periphery of the connection of the stirring portion and the cylindrical portion has the same wall thickness as that.
Moreover, the wall thickness of the flexible portion is formed so as to form the thin-walled portion and the thick-walled portion in the circumferential direction toward the cylindrical portion from the stirring portion radially alternately.
Furthermore, in one which the thin-walled portion and the thick-walled portion are formed radially, the ratio of the thin-wall thickness versus the thick wall thickness of the flexible portion is set at 1.0:1.1 to 1.0:5.0.
Although the ratio of the thin wall thickness versus the thick-wall thickness of the flexible portion according to the invention depends upon the size of the damper and the strength of the elastic body like rubber or the like, it is preferably within the range of 1.0:1.1-1.0:5.0. The change in the thickness does not appear on the change in the spring constant as the damper, when the wall thickness of the thick walled portion with respective to the wall thickness of 1.0 of the thin-walled portion is smaller than 1.1, on the one hand, the difference in tensile stress strength of the thin-walled portion and the thick-walled portion appears remarkably, when being larger than 5.0, and only the thin-walled portion can oscillate even though the amplitude becomes large, whereby it does not appear on the change in the spring constant. The ratio of the wall thickness is preferably within the range of 1.0:1.5-1.0:3.0.
In the flexible portion according to the invention, the wall thickness on a circumference of a concentric circle is formed equally outwardly from the flexible portion, and since the wall thickness in the thin-walled portion is thin, the spring constant is small, moreover, since the wall thickness in the thick-walled portion is thick, the spring constant is large. For the constitution of the wall thickness according to the invention, in the arrangement of the thin-walled portion and the thick-walled portion, any one there of may be arranged on the inner periphery side, moreover, for a manner of the change in the thickness, either of the change which varies successively or in stages, or the change which has the boundary and the thickness is switched.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.